1. Field of the Invention
The present invention relates to a digital camera having an exposure mode (e.g., bulb mode) that is used for long exposures (e.g., an exposure for several seconds or longer).
2. Description of the Related Art
Some digital cameras have an exposure mode in which the shutter remains open for several seconds or longer, e.g., a bulb mode in which the shutter remains open as long as the shutter release button is held down or a slow shutter mode in which the shutter is released at a shutter speed slower than a normal shutter speed. Prior to an exposure operation (photographing operation) in such an exposure mode, a battery check process is generally performed to prevent the camera from malfunctioning due to a battery voltage drop of the digital camera. In the battery check process it is determined whether the battery voltage is below a predetermined voltage level (battery-check level), and an exposure operation is allowed to be performed only when it is determined that the battery voltage is equal to or higher than the battery-check level. If it is determined that the battery voltage is lower than the battery-check level, a warning (e.g., a warning indication) is issued in order to warn the user that the battery is flat (i.e., having insufficient power) to urge the user to replace the battery with a new one, and/or prohibits further use of the flat battery.
However, there is a possibility of the battery voltage dropping below the battery-check level during exposure in slow shutter mode or bulb mode, even if it is determined that the battery voltage is equal to or higher than battery-check level before exposure. This is because the exposure time in such an exposure mode is usually much longer than a normal exposure time. In conventional digital cameras, all the operations are forcibly terminated once the battery voltage drops below the battery-check level even during exposure, which makes it impossible to capture a desired digital image in such circumstances. Consequently, a photographing operation in such a long exposure mode ends up in failure.